Do you like report designs that look like this?

Me neither. It may print the right data, but it’s difficult (= expensive) to maintain.

Fortunately you can easily show something descriptive instead of «Expr». Right-click the value and pick Placeholder Properties…

and type a description of the placeholder to Label:

The designer will then display the description instead of «Expr»:

You surely don’t want to go and change all existing reports with this problem, but I encourage you to do it for all new development.